1. Field of the Invention
The present invention relates in general to the field of electronic circuits, and more particularly to a system and method for flexible circuits, such as flexible circuits that interface a portable computer with a display lid.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally process, compiles, stores and/or communicates information or data for business, personal or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored or communicated, and how quickly and efficiently the information may be processed, stored or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store and communicate information and may include one or more computer systems, data storage systems, and networking systems.
One difficulty that arises with information handling systems is the interfacing of components that move relative to each other. Flexible printed circuits are generally used for such interfaces and allow bending of the circuit by disposing signal wire lines in a flexible material. However, in order provide sufficient flexibility without excessive size, flexible printed circuits have reduced insulation resulting in problems transmitting signals without excessive electromagnetic interference emissions. For example, flexible printed circuits are often used to interface a portable computer display integrated in a lid with the main body of the portable computer. The use of a flexible printed circuit having sufficient flexibility allows repeated open and close cycles of the lid.
As portable computer designs have improved, the displays used by portable computers have achieved improved resolution, recently reaching resolutions of 1600×1200 with the UXGA and LVDS standards. However, the improved resolution has resulted in greater data transfer needs across flexible printed circuits, increasing the difficulty of transferring display signals without undue interference. For instance, display signal transfer rates have increased from the 65 MHz single channel rate of the XGA standard to the 54 MHz dual channel rate of the SXGA standard and the 80 MHz dual channel rate of the UXGA standard. This increase in display signal data transfer rates has presented a difficulty in accurate data transmission over sufficiently flexible circuits without breakage of wires in the flexible circuits from stress related to lid movement.
In order to obtain adequate signal transfer with sufficient flexibility, a variety of ground planes have been incorporated with flexible printed circuits. For instance, a silver ink, silver mesh or copper mesh imaging ground plane has been added to the flexible circuit, sometimes with randomly disposed wire lines, to reduce ground resistance and to reduce inductance generated by signal wires. However, flexible printed circuits remain susceptible to breakage due to dynamic bending and the ground planes have provided inadequate high-speed signal imaging. In addition, differences in resistance of ground plane material compared with signal resistance and interface resistance have left high inductance of the ground plane and large junction impedance in the ground plane transition into and out of the flexible circuits. The use of an inadequate ground plane results in excessive emissions and poor display signal data transfers, particularly as display data transfer rates have increased.